Hydropneumatic suspensions are used, for example, as rear-axle suspensions in tractors or other machines. If a fluid-carrying connection is established between a suspension accumulator and a suspension cylinder by the pilot-actuated valve, especially one in the form of a conventional hydraulic accumulator or working cylinder connected to the respective wheel set of the tractor or machine, the wheel axis for the respective operating application is correspondingly spring-suspended. If it is now desired to use the machine, especially one in the form of a tractor, to carry out operating processes such as plowing of a field with plowing equipment, the suspension is to be blocked. Specifically, the connection between suspension cylinder and suspension accumulator is interrupted by the pilot-actuated valve. This arrangement presents the advantage that the “working height” of the plow or other equipment may not be changed unintentionally, something which might impair the respective application intended.
The known technical solutions, such as are commercially available, normally employ purely electric actuation of the pilot-actuated stop valve for the associated stopping of the hydropneumatic suspension. Since this pilot-actuated valve is configured to be quite large in view of the volumes of flow to be controlled, high actuating forces are required to switch the valve. The high-switching forces in turn lead to use of switching magnets of correspondingly large size for actuation of the valve, and require correspondingly high electric power consumption. In addition, when the hydropneumatic suspension is at rest with the pilot-actuated valve in its blocked position, the respective drive configuration is rigid by design and effects exerted on the operating equipment, for example, by uneven ground over which the tractor or machine is operated, cause respective disruptive influences. Such disruptive influences are transmitted to the operating equipment, such as a plow, and may significantly impair the plowing process itself. The vehicle is designed to be more rigid from the viewpoint of its driving behavior than control of the plow and permits for an operating process, such as plowing or the like. In known solutions during the unblocking process, which takes place rapidly, any difference in pressure between suspension cylinder and pressure accumulator which may be present is very quickly equalized, resulting in “bouncing” of the vehicle.
The proximate state of the art in the form of DE 42 42 448 C1 relates to a hydropneumatic suspension assembly for vehicles with high load ratios, in particular for tractors with means for mounting cultivators and load-sensing pumps for pressure generation. Pressure also is applied to the annuli of the suspension cylinders connected to a hydraulic accumulator. Known configurations of this type have control mechanisms which must be fed by constant-pressure systems. The use of a load-sensing pump is of no avail, since it would always have to deliver against high pressure. These known systems also present the disadvantage that they continuously consume energy. According to the solution disclosed in DE 42 42 448 C1, conservation of energy and the possibility of using a load-sensing pump are achieved in that the annulus is supplied with pressure by a 3-way pressure control valve and in that a level control assembly having a valve assembly is provided. The level control with its valve assembly is briefly activated and deactivated only when static load changes occur and removes pressure from all control and feed lines in the position at rest which is otherwise assumed. The piston chambers and annuli are hermetically sealed off by return valves that may be unblocked.
Even with this known solution, the possibility is not excluded of movements occurring unintentionally at the vehicle during the unblocking process because of the pressure difference which may be present.